This invention relates to the field of meters and particularly to the field of meters for measuring the concentration of water in a water-ink mixture.
Lithographic printing presses use a mixture of ink and aqueous dampening solution. The dampening solution is water with small amounts of proprietary additives to enhance water wetting of the printing plate. A continuous flow of ink and of dampening solution are furnished to the press. These can be supplied as a mixture of ink and dampening solution; or as separate streams of ink and dampening solution depending upon press configuration. In any case, the useful printing mixture on press contains both ink and water. In keyless inking systems, for economical operation, the ink-water mixture could be recirculated, since only a fraction of the ink mixture is being consumed by the printing process at any given time.
In order to obtain the best printing results, the proper amounts of water and of ink in the mixture must be maintained. This can be done at start-up when a fresh water-ink mixture is added by using the proper proportions for making the mixture. However, over a period of time during printing the proportions of ink and water can change in the recirculating mixture. At present, the printer attending the press has no means of automatically and continuously monitoring the concentration of water in a recirculating water-ink mixture. He must rely upon his experience and the printing results to estimate the concentration of the water in the mixture.
Meters are known which measure the dielectric constant of a mixture to determine the moisture content of materials or the density of a mixture. Some of these prior art meters use a Wheatstone bridge-type circuit to measure dielectric properties (e.g., U.S. Pat. No. 3,696,299). Other use two oscillators to obtain a frequency differential which is related to the dielectric properties of the material being tested (e.g., U.S. Pat. No. 4,048,844). Still other meters use an oscillator with peak detectors (e.g., U.S. Pat. No. 4,399,404) or a logic circuit (e.g., U.S. Pat. No. 4,130,796). However, what the printer needs is a simple meter which will automatically provide a direct reading of the concentration of water in the ink.